The two most important principles of quantum computing
We’ve already talked about qubits, but there are a few other key concepts necessary to understand quantum computers and how they work.
1. Superposition
The first concept to understand is the concept of superposition. We alluded to the idea of superposition earlier, where we noted that a qubit can store the state of both on and off simultaneously. This is known as a superposition, and it is core to the concept of quantum computing.
To easily imagine superposition, consider the idea of an employee working on a project. It’s right around lunchtime, so you know that they’re either at their desk working, or they’re in the breakroom, heating up their lunch — but until you check, you can’t say which.
In quantum terms, we'd say the employee is in a superposition of the breakroom and their desk. Intuitively, you might think that the employee must be in one place or the other, and technically they are; an employee cannot be in both places at once. But subatomic particles don’t operate by the same rules that human employees do. Experiments over the past several decades have confirmed this repeatedly: quantum systems genuinely hold multiple possibilities at once, rather than concealing a single predetermined one.
Superposition is what gives quantum computers their reach. Ten qubits span 1,024 possible states at once — a space that would take 1,024 separate classical values to represent.
But that's not the same as running 1,024 calculations and reading off the best one. When you measure a quantum system, you get a single answer. The art of quantum algorithm design is arranging the computation so that the paths leading toward wrong answers cancel each other out and the paths leading toward the right answer reinforce, a property called interference. Run the circuit enough times and the correct answer emerges as the dominant result.
This is why quantum computers aren't simply faster computers. The speedup only materializes for problems with the right mathematical structure. For most of what computers do every day, a quantum machine offers no advantage at all.
2. Entanglement
We’ve covered quantum superposition, and the other critical concept related to that is entanglement. Superposition means that a qubit can be in multiple states at the same time. Entanglement means that the state of one qubit (or other subatomic particle) is directly tied to the state of another qubit.
To imagine this, let’s look back to our previous example of an employee at work. Say we have two employees, Alice and Bob, splitting desk coverage: one works while the other takes lunch. If you don't know whose break it is, either could be in either place. Walk to the desk, find Bob working, and you instantly know Alice is in the breakroom.
Entangled qubits produce correlations like this, but stronger than any schedule could explain. Alice and Bob worked out their arrangement in advance; the information existed before you looked. Entangled qubits carry no such prior agreement. Experiments confirming this, recognized with the 2022 Nobel Prize in Physics, ruled out the possibility that entangled particles are simply hiding pre-set answers.
Measurement is where the two ideas meet. When a qubit in superposition is measured, it resolves into a definite state, either on or off, no longer both. This is called collapse. In an entangled pair, collapsing one qubit determines the other immediately, no matter how far apart they are.
Collapse is what makes a quantum program readable. The algorithm builds up a superposition across many entangled qubits, interference sharpens the useful outcomes, and measurement collapses the system into a set of classical bits you can actually read. Run the program repeatedly and the correct answer surfaces as the most frequent result.
